Treatment of some spinal injuries or disorders may involve the use of a spinal fixation element, such as a relatively rigid fixation rod, that is coupled to adjacent vertebrae by attaching the element to various anchoring devices, such as plates, hooks, bolts, wires, or screws. Often two rods are disposed on opposite sides of the spinous process in a substantially parallel relationship. The fixation rods can have a predetermined contour that has been designed according to the properties of the target implantation site, and once installed, the rods hold the vertebrae in a desired spatial relationship, until healing or spinal fusion has taken place, or for some longer period of time. When such surgery is performed in the cervical spine, the proximal ends of the rods are typically molded according to the anatomy of the skull and the cervical spine, and attached to a fixation plate that is implanted in the occiput.
There are currently two types of plates that are typically used in the occiput: a T-shaped plate and a Y-shaped plate. The T-shaped plate is designed to maximize the amount of bone graft that can be disposed between the cervical spine and the foremen magnum. When implanted, its shape requires that it be positioned just below the superior nuchal line. As a result, the rod-to-plate connection occurs at a higher location in the occiput, thus becoming more noticeable to the patient. The Y-shaped plate, on the other hand, is configured to sit below and just inside of the inferior nuchal line. Thus, the rod-to-plate attachment occurs at a lower position in the occiput, thereby providing a low-profile connection that is less noticeable to the user. However, because the area between the cervical spine and the occiput is greatly reduced, the use of bone graft material with the Y-shaped plate is limited.
While these plate constructs have provided a stable technique for occipito-cervical fixation, fixation to the occiput continues to be a challenge. In particular, extreme variability in the thickness of the skull itself can limit the effectiveness of current plates, which must be positioned at a particular location in the occiput, even if such a position is not optimal. As a result, the effectiveness of the plate is largely dependent on the positioning of the holes in the plate, as the fixed hole-hole distances in the plate can make proper insertion of the screws difficult. Other complications associated with any internal fixation device, such as hardware loosening, hardware pull out, and hardware fracture, for example, can also occur.
Accordingly, the present invention advantageously provides a spinal fixation plate that can be placed in various locations in the occiput, thus allowing the plate to be implanted at the thickest bone for increased safety as well as optimal stability.